The present invention relates to telemetry systems for communicating information. The invention finds particular application in telecommunication systems for monitoring pressure and other conditions at submerged petroleum production equipment and will be described with particular reference thereto. It is to be appreciated, however, that the invention finds other applications in conjunction with monitoring conditions at remotely positioned transducers in other environments.
Heretofore, transducers have been used to monitor pressure, temperature, and other system variables. For accurate measurements in severe environments, instrumentation tubing commonly carried fluid from the severe environment to electronic monitoring instrumentation in a more hospitable location. However, the instrumentation tubing was vulnerable to damage and corrosion which could cause it to lose fluid to the environment.
Commonly, the remotely located monitoring instrumentation received power from and transmitted condition indicative signals to a central location. Many prior art systems used separate wires to provide electrical power to the montoring instrumentation and to carry montored data from the instrumentation to the central location. However, others have suggested utilizing the same wire for both purposes. Although various techniques have been suggested for carrying the condition data on the power lines, such techniques commonly require ohmic paths connecting the remote monitoring instrumentation with the central power supply and condition display units. Such techniques are ineffective for transferring data across inductive couplings. For safety and ease of connection and disconnection, inductive couplings are standard in subsea installations. Both electrical power and instrumentation signals must be transferred across the inductive couplings.
The present invention contemplates a new and improved method and apparatus for conveying power and analog signals over a single pair of wires and across one or more inductive couplings.